Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking

[Peter Lieven <pl@dlhnet.de>]

Am 06.03.2013 19:48, schrieb Jeff Cody:
> On Wed, Mar 06, 2013 at 07:31:51PM +0100, Paolo Bonzini wrote:
>> Il 06/03/2013 19:14, Jeff Cody ha scritto:
>>> QCOW breaks with it using a normal raw posix file as a device.  As a
>>> test: qemu-img create -f qcow test.qcow 5G.  Now run qemu with that
>>> drive mounted, and try to partition and format it.  QEMU now asserts.
>>>
>>> The nicety of being able to using truncate during a write call,
>>> especially for VHDX (which can have relatively large block/cluster
>>> sizes), so to grow the file sparsely in a dynamically allocated file.
>>
>> Perhaps we need two APIs, "truncate" and "revalidate".
>>
>> Truncate should be a no-op if (!bs->growable).
>>
>> Revalidate could be called by the block_resize monitor command with no
>> size specified.
>>
>> Paolo
> 
> I think that is a good solution.  Is it better to have "truncate" and
> "revalidate", or "truncate" and "grow", with grow being a subset of
> truncate, with fewer restrictions?  There may still be operations
> where it is OK to grow a file, but not OK to shrink it.
> 

Or as a first step:

a) Call brdv_drain_all() only if the device is shrinked (independently of !bs->growable)
b) Call brdv_drain_all() inside iscsi_truncate() because it is a special requirement there
c) Fix the value of bs->growable for all drivers

Peter